The present invention relates to a method for collectively transmitting and collecting communication information in an information transmission system, and a system using the method.
As the information transmission system, a digital data bus (D.sup.2 B) for communicating information between audio/video equipments has been known (IEC "84 Secretariat 47 Draft Peritelevision/D.sup.2 B"). The conventional D.sup.2 B information transmission system has a function to communicate one information message from one source communication control unit connected to an information transmission line to one destination communication control unit connected to the information transmission line in one-to-one communication fashion.
FIG. 8 shows a block diagram of a prior art information transmission system. Numeral 101 denotes an information transmission line for transmitting information messages, and numerals 102 and 103 denote communication control units for mutually communicating through the information transmission line.
FIG. 9 shows a format of a conventional information message. It comprises a start bit indicating the beginning of the information message, a master address indicating a source address, a parity bit indicating a parity of the master address, a slave address indicating a destination address, a parity bit and an ACK bit indicating a parity of the slave address, a control field indicating an attribute of the information message, a parity bit indicating a parity of the control field, and a data field indicating transmission information. The parity bit is used for parity check. The ACK bit informs to the transmitter whether the receiver has normally received the data or not. If the receiver normally receives, it sends back an acknowledge (ACK) signal, and if it incorrectly receives, it sends back a non-acknowledge (NACK) signal.
A communication method in the above system is explained. When an information message is to be sent from the communication control unit 102 to the communication control unit 103 in FIG. 8, the communication control unit 102 first send the start bit, and then send a unit address of the communication control unit 102 as the master address, the parity bit thereof, a unit address of the communication control unit 103 as the slave address, and the parity bit thereof. The unit addresses of the communication control units 102 and 103 are uniquely present on the information transmission line 101. When the communication control unit 103 detects the start bit, it starts to receive the information message to receive the master address, the parity bit thereof, the slave address and the parity bit thereof. If the information message is normally received and the slave address coincides with the unit address of the communication control unit 103, the communication control unit 103 determines that the information massage is addressed to its own unit and sends back the ACK bit. If it does not correctly receive the information message by asynchronization or parity error during the receiving operation, or if the slave address does not coincide with the unit address of its own, it sends back the NACK bit. If the communication control unit 103 is not connected to the information transmission line 1, the ACK bit is not sent and no response is sent. The communication control unit 102 determines it as if it received the NACK bit. When the communication control unit 102 receives the NACK bit, it stops to send the information message. When the communication control unit 102 receives the ACK bit, it further sends the control field and the parity bit thereof. When the communication control unit 103 correctly receives the control field and the parity bit thereof, or when it is able to execute the operation designated by the control field in the receiving station, it sends back the ACK signal. If it does not correctly receive the control field and the parity bit thereof because of asynchronization or parity error during the receiving operation, or if it cannot execute the operation designated by the received control field, it sends back the NACK signal to the communication control unit 102. When the communication control unit 102 receives the NACK signal, it stops to send the information message. When it receives the ACK signal, it further transmits the data field to the communication control unit 103.
Collective collection of information by one of the communication control units connected to the information transmission line is now considered. In a bus type communication network shown in FIG. 12 in which a plurality of communication control units are interconnected through an information transmission line, let us assume that a communication control unit 105 receives information .circle.1 of a communication control unit 106 and information .circle.2 of a communication control unit 107 through an information transmission line 104. Numerals in &lt; &gt; in the respective communication control units represent unit addresses on the information transmission line assigned to the respective communication control units. A communication message and a communication sequence therefor are shown in FIGS. 13 and 14, respectively. The communication control unit 105 designates an address of a memory, in which the information to be read from the communication control unit 106 is stored, by a communication message shown in FIG. 13a, in which MA denotes a master address which is a source address, and SA denotes a slave address which is a destination address. The unit address &lt;200&gt; of the communication control unit 105 and the unit address &lt;210&gt; of the communication control unit 106 are designated. CF denotes a control field which represents an attribute of the message. Specifically, it has a code which indicates the attribute of the memory address designation. In the following data field, an address of the memory in which the information to be read is stored is written. The communication control unit 105 then reads the information from a memory 108 of the communication control unit 106 by a message shown in FIG. 13b, in which MA contains the unit address &lt;200&gt; of the communication control unit 105, AS contains the unit address &lt;210&gt; of the communication control unit 106, and CF contains a code indicating the read-out of the data. When the communication control unit 106 receives the code, it detects the data read-out code and sends back the information .circle.1 stored at the address designated by the memory address designation message of FIG. 13a, as a data field of the data read-out message of FIG. 13b. When the communication control unit 105 reads the information .circle.2 from the information memory 109 of the communication control unit 107, it reads the information by a memory address designation message of FIG. 13c and a data read-out message of FIG. 13d . FIG. 14 shows a communication sequence in reading the data by the messages of FIGS. 13a, 13b, 13c and 13d.
In the prior art communication control method mentioned above, when one communication control unit communicates the same information with a plurality of communication control units, it has to repeatedly communicate the same information message to the plurality of communication control units. Thus, a procedure is very complex.